Vibrational spectroscopy of individual surface adsorbates

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The purpose of the present research was to develop the method that makes it possible to determine the vibrational energies of individual species adsorbed on solid surfaces. For this purpose, we investigated scanning tunneling microscope (STM)light emission spectra of adsorbates. We have found that vibrational motions of the adsorbate being located beneath the tip are excited through two channels in the STM light emission process. One is the direct excitation by the tunneling current and the other is that by localized surface plasmons (LSP) being excited by the tunneling currant. When the Former channel is dominant, periodic fine structures are seen in the STM light emission spectra. Since the period of tine fine structures agrees with the vibrational energy of the absorbate, one can determine its value through the Fourier analysis of the STM light emission spectra. When the latter channel (i.e, excitation by LSP) is dominant; stepwise structures appear at the vibrational energies below … More the quantum cutoff in the STM light emission spectra. The value of the quantum cutoff is determined by the measurement condition. Hence, one can also know the vibrational elegies from the latter channel.. Theoretical investigations show that the periodic fine structures are reproducible in the framework of the currant fluctuation theory of STM light emission. The stepwise structures can be understood as a kind of Raman scattering of LSP by the adsorbate. The vibrational modes that can be determined by the present method were also explored, those of hydrogen atoms, oxygen atoms, and single molecules of benzene adsorbed on various lands of substrates including Ni, Cu, and Ag were deduced from the STM light emission spectra. Furthermore, we succeed in determining the phonon energies of substrate itself from the STM light emission spectra. This result shows that the present method is applicable to vibrational spectroscopy of not only adsorbates but also solid materials (e g., nano-materials). Less